A brake is typically a mechanical device designed to inhibit motion. Brakes commonly use friction to convert kinetic energy into heat, though other methods of energy conversion may be employed. For example, regenerative braking converts much of the energy to electric energy, which may be stored for later use.
On vehicles, braking systems are employed to apply a retarding force, typically via frictional elements at the vehicle's rotating axles or wheels, to inhibit vehicle motion. Friction brakes often include shoes or pads lined with friction material for engagement with a rotating wear surface, such as a rotor or a drum. Common configurations include shoes that contact and rub on the outside of a rotating drum, commonly called a “band brake”, a rotating drum with shoes that expand to rub the inside of a drum, commonly called a “drum brake”, and pads that pinch a rotating disc, commonly called a “disc brake”.
Disc brakes generally employ brake calipers that are mounted to a vehicle suspension and use hydraulic force to press the aforementioned shoes or pads against the respective rotating disc, to thereby pinch the disc and slow the attendant wheel. Calipers come in two general types, floating and fixed. A fixed caliper does not move relative to the disc and is thus less tolerant of disc imperfections. The fixed caliper uses one or more pistons from one side, or one or more pairs of opposing pistons to clamp the rotating disc from each side thereof. A floating or sliding caliper moves with respect to the disc, along a line parallel to the axis of rotation of the disc. In such a case, a piston on one side of the disc pushes the inner brake pad until it makes contact with the braking surface, then pulls the caliper body with the outer brake pad so pressure is applied to both sides of the disc.